Transcript distributed database architecture and database link

DATABASE LINK
DISTRIBUTED DATABASE
OVERVIEW DATABASE LINK
Some DBMS like Oracle have a way to
communicate each other
 This communication can be built by means
database link
 A database link is a pointer that defines a oneway communication path from an Oracle
Database server to another database server
 The link pointer is actually defined as an entry in
a data dictionary table

OVERVIEW DATABASE LINK (CONT’D)
A database link connection allows local users to
access data on a remote database
 Each database in distributed system must have
unique global database name in a network
domain

DATABASE LINK
DATABASE LINK TYPE

Private database link
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
Public database link


All user can have access to database link
Global database link


Only Db link creator can have access to database link
– only user
Can access data and db object
User access a remote database through the
following of link
Connected user link – connected as them self – same
user name and password
 Fixed user link – connect from different user
 Current user link – connects as global user

SHARED DATABASE LINK

Link between local server process and remote
database
GLOBAL DATABASE NAME
Each database in a distributed database is
uniquely identified by its global database name
 The database forms a global database name by
prefixing the database network domain
 Specified by the DB_DOMAIN initialization
parameter at database creation

GLOBAL DATABASE NAME
GLOBAL DATABASE LINK SINTAX
ORACLE CONNECTIVITY CONCEPTS

There are two main objects in database
connectivity
Database Service
 Database Instance

DATABASE SERVICE
Oracle database is represented to clients as a
service
 Database can have one or more services
associated with it

DATABASE SERVICE (CONT’D)

A database can have multiple services associated
with it
DATABASE SERVICE (CONT’D)

Multiple service can have following
functionalities
A single database can be identified in a number of
different ways by different clients
 A database administrator can limit or reserve system
resources

DATABASE INSTANCES
A database has at least one instance
 An instance is comprised of a memory area called
the System Global Area (SGA) and Oracle
background processes
 The memory and processes of an instance
efficiently manage the associated database's data
and serve the database users

DATABASE INSTANCE (CONT’D)

Single Instance
DATABASE INSTANCE (CONT’D)

Multiple Instance
HOW CLIENT AND SERVER COMMUNICATE
To connect to a database service, clients use a
connect descriptor that provides the location of
the database and the name of the database
service
 Example of configuration

ORACLE NET SERVICE

Stack Communication for client/server connection
ORACLE NET SERVICE (CONT’D)

Stack communication for java application
ORACLE NET SERVICE (CONT’D)

Stack communication for web client
LISTENER ARCHITECTURE

The database server receives an initial
connection from a client application through the
listener. The listener is an application positioned
on top of the Oracle Net foundation